C. difficile is the most important cause of nosocomial intestinal infections and is the major cause of pseudomembranous colitis in humans (Bartlett et al Am. J. Clin. Nutr. 11 suppl: 2521-6 (1980)). The overall associated mortality rate for individuals infected with C. difficile was calculated to be 5.99% within 3 months of diagnosis, with higher mortality associated with advanced age, being 13.5% in patients over 80 years (Karas et al Journal of Infection 561:1-9 (2010)). The current treatment for C. difficile infection is the administration of antibiotics (metronidazole and vancomycin), however there has been evidence of strains which are resistant to these antibiotics (Shah et al., Expert Rev. Anti Infect. Ther. 8(5), 555-564 (2010)). Accordingly there is a need for immunogenic compositions capable of inducing antibodies to, and/or a protective immune response to, C. difficile. 
The enterotoxicity of C. difficile is primarily due to the action of two toxins, toxin A (‘ToxA’) and toxin B (‘ToxB’). The C-terminal domains of toxin A and toxin B comprise repeating units, for example the C-terminal domain of toxin A is made up of contiguous repeating units (Dove et al Infect. Immun. 58:480-499 (1990)). For this reason the C-terminal domain may be referred to as the ‘repeating domain’. These repeat portions can be separated further into short repeats (SRs) and long repeats (LRs) as described in Ho et al (PNAS 102:18373-18378 (2005)).
Immunogenic compositions comprising antigens from C. difficile have been described. WO96/12802 and WO00/61762 and Lyerly et al (Current Microbiology 21:29-32 (1990)) relate to fragments of toxin A, in particular fragments of the C-terminal domain, for inducing a protective immune response in hamsters. WO9920304 relates to a mixture of co-purified toxin A and toxin B inactivated by incubation in formaldehyde. WO00/61762 relates to immunogenic compositions comprising either the full length C-terminal domain or fragments of the C-terminal domain of toxin A and toxin B of C. difficile. Similarly WO2012/163817, WO2012/163811 and WO2012/163810 provide disclosures of possible fragments of toxin A and toxin B as well as fusion proteins thereof.
New compositions or vaccines with improved immunogenicity are needed. As one strategy, adjuvants have been used to try and improve the immune response raised to any given antigen. For example, WO2009035707 describes a composition comprising a toxoid of C. difficile toxins A and B and an adjuvant such as aluminum hydroxide compound.
Adjuvants containing combinations of lipopolysaccharide and Quillaja saponins have been disclosed previously, for example in EP0671948. Oil in water emulsions per se are well known in the art, and have been suggested to be useful as adjuvant compositions (EP 399843; WO 95/17210).
There is still a need for vaccine and immunogenic compositions that provide a suitable immune response against C. difficile. 